Drilling activity in hard and tight Shale formations has increased substantially in the last few years. The wells that are drilled in these formations are generally very deep and complex. They can be comprised of depths that may exceed 10,000 feet vertically and 10,000 feet in the lateral section of the well.
During the drilling operation of these wells, which may include, but are not limited to, tripping in and tripping out of the well, sliding, rotation, etc., the drill pipe is subjected to high compressive loads that could cause severe buckling of the drill pipe. The buckling could manifest itself as Helical Buckling in the vertical section and/or Sinusoidal Buckling in the lateral section. Sinusoidal buckling occurs when the axial force on a long column, in this case drill pipe, exceeds the critical buckling force and the pipe elastically deforms or bends and takes on a snake-like shape in the hole. Weight transfer is still possible during Sinusoidal Buckling, but is inefficient. Additional compressive loads cause Sinusoidal buckling to transition to Helical Buckling, and take on a corkscrew-like shape in the hole. As such, Helical Buckling is more severe and occurs after Sinusoidal buckling.
Helical Buckling may or may not cause plastic or permanent deformation of the pipe, depending upon the amount of axial compressive forces applied, although most buckling stresses are below the yield strength of the pipe. In its most severe form, Helical Bucking can result in Helical Lockup, which is when weight can no longer be transferred to the bit.
The critical buckling load of drill pipe is not only dependent on drilling conditions, such as drill pipe size and hole size, but also and more important is whether the wellbore is straight, horizontal, curving, or inclined. In highangle wells, the force of gravity pulls the drill string against the low side of the hole. This helps to support and constrain the pipe along its length, stabilizing the string and as a result, allowing the drill pipe to withstand higher axial loads before buckling.
Inversely, vertical sections are the most susceptible to buckling. Critical compression in the vertical section of the hole can result in buckling. In build sections, the bending forces exerted by the hole help the pipe to resist buckling. However, pipe will always buckle first in a straight section.
Buckling also causes an increase in drill pipe casing contact and wellbore drill pipe contact. Along with the increased contact, the drill pipe also sees increased side force due to buckling on these contact areas. The more weight applied at surface, the more the coiled pipe presses into the sides of the hole—which has lead many in the industry to support the belief that bucking causes excessive tube wear.
Buckling not only can damage the pipe, it can also negatively affect drilling operations. In slide drilling, for example, buckling may prevent the desired weight on bit because of an increase in drill string side loads to the point that weight cannot be efficiently transmitted to the bit. At the same time, side loads are increased by buckling of the drill pipe due to compressive loading, further exacerbating the problem.
Ultimately, due to the severe drilling environment in downhole wells, the useful life of the drill pipe is severely shortened. In addition to buckling, the drill pipe may exhibit severe abrasion on one side of the tool joint following the failure of the hardbanding, which will lead to wall thickness loss at the tool joint and/or washouts at the middle section of the tubes.
In view of the foregoing, there is a need in the art for a method by which the useful life of the drill pipe is extended against downhole abrasions and buckling, thereby providing a drill pipe having increased wear and buckle resistance.